A wide variety of lipases of microbial and mammalian origin are known. The amino acid sequence of many of these lipases have been elucidated and analyzed with respect to structural and functional elements important for their catalytic function, see, for instance, Winkler et al., 1990 and Schrag et al., 1991. It has been found that the lipase enzyme upon binding of a lipid substrate and activation undergoes a conformational change, which inter alia, results in an exposure of the active site to the substrate. This conformational change together with the presumed interaction between enzyme and substrate have been discussed by, inter alia, Brady et al., 1990, Brzozowski et al., 1991, Derewenda et al., 1992.
Based on the knowledge of the structure of a number of lipases, it has been possible to construct lipase variants having improved properties by use of recombinant DNA techniques. Thus, WO 92/05249 discloses the construction of certain lipase variants, in which the lipid contact zone has been modified so as to provide the variants with different substrate specificities and/or an improved accessibility of the active site of the lipase to a lipid substrate. The modifications involve changing the electrostatic charge, hydrophobicity or the surface conformation of the lipid contact zone by way of amino acid substitutions.
Although the structural and functional relationship of lipases have been the subject of a number of studies as described in the above cited references, the research has mainly focused on the macroscopic characteristics of the lipases upon substrate binding and activation, whereas the identity of the amino acids actually involved in the substrate binding and catalytic activity has been discussed only to a lesser extent.